Posted
by
Soulskill
on Saturday December 10, 2011 @11:20AM
from the i-think-captain-kirk-disproved-this dept.

Hugh Pickens writes "Planetary scientists say there are aspects to our planet and its evolution that are remarkably strange. In the first place there is Earth's strong magnetic field. No one is exactly sure how it works, but it has something to do with the turbulent motion that occurs in the Earth's liquid outer core and without it, we would be bombarded by harmful radiation from the Sun. Next there's plate tectonics. We live on a planet that is constantly recycling its crust, limiting the amount of carbon dioxide escaping into the atmosphere — a natural way of controlling the greenhouse effect. Then there's Jupiter-sized outer planets protecting the Earth from frequent large impacts. But the strangest thing of all is our big Moon. 'As the Earth rotates, it wobbles on its axis like a child's spinning top,' says Professor Monica Grady. 'What the Moon does is dampen down that wobble and that helps to prevent extreme climate fluctuations' — which would be detrimental to life. The moon's tides have also made long swaths of earth's coastline into areas of that are regularly shifted between dry and wet, providing a proving ground for early sea life to test the land for its suitability as a habitat. The 'Rare Earth Hypothesis' is one solution to the Fermi Paradox (PDF) because, if Earth is uniquely special as an abode of life, ETI will necessarily be rare or even non-existent. And in the absence of verifiable alien contact, scientific opinion will forever remain split as to whether the Universe teems with life or we are alone in the inky blackness."

That's just science at work, and every theory has it's "difficulties" answering all of our questions. The fact that this particular wiki article has a "Difficulties" section doesn't disprove the scientific merit of the giant impact theory, it proves that the wiki writer tried to give a complete picture and wanted to list some of the interesting questions still out there. Simply put, the giant impact hypothesis has no rival that provides as many self consistent lines of reasoning right now.

Didn't the Earth get hit by another planet, causing it to shoot a ton of crust into orbit..creating the moon?

That's one going theory, but there are good arguments for orbital capture also. The biggest one being the concentration of elements on the moon is different than those found on earth. The moon has a LOT of silicon on it for example, and very little carbon. If it was created by the splash from an impact, one would expect it to have at least a similar concentration of elements as the parent body. Elemental concentration doesn't change a lot over the course of a planet's existence, since elements are formed within stars and planets have to play with the hand they were dealt when they formed. Comets may bring in a little, and atmosphere may bleed away, but the lion's share of the ratio remains unchanged from beginning to end.

Right now the big hangup on that is we don't know a lot about the interior of the moon, other than it's solid. It's possible the surface of the moon just happened to wind up being mostly Si, and the interior is more of an earth-like distribution of elements. But when planets cool, heavy things go to the core and light things float on top, which is why earth has lots of carbon on the crust and iron in the core. You'd expect the same of the moon.

There's more. The "uniquers" are clueless. Is the magnetic field because of our unique liquid core?

No. We have a lot of iron and rotate. Duh.

Moons! Look at the moons! Statistically most of the other rocks going around the sun have 'em, too.

And so forth. Statistically, we're in a zone that allowed the chemicals to make whoopee and produce life, leading to us. People believe they're special, but they evolved something that they narcissitically believe is "intelligence". Do they treat their little planet with care? I don't think so. And they kill each other with glee, and deny the world around them, waiting for magical-thinking to become real.

Yup, but only Earth has a moon we don't "deserve", given our size. No other planet in the solar system has any moon even remotely as large as ours compared to its own mass. At least since Pluto has been demoted.

Yes, yes, yes, all the things that happened here are so incredibly unlikely to happen... but then again, the universe is incredibly large and here the law of the large number fits perfectly: NO matter how insignificantly unlikely something is, if there is ONE case where it is true and your sample size is (nearly) infinitely large, the chance to find another case is 1.

if there is ONE case where it is true and your sample size is (nearly) infinitely large, the chance to find another case is 1.

Perhaps "nearly 1", but not 1. Case in point: There are infinite counting numbers, but only 1 even prime number (2). Surely with an infinite sample size, by your logic, you would expect multiple examples even primes?

There are 400 billion stars in our galaxy, and there are probably many billions of planets. Out of all those possibilities, how rare could it be for a planet to be in the "habitable zone" of a star, with a few gas giants farther out? And isn't iron a fairly common element in planets, hence molten core, hence magnetic field protecting the surface from cosmic rays and all that.

If we suppose that Earth-like conditions are one in a billion, which seems exceedingly conservative, nonetheless we're talking about dozens or hundreds of Earth-like planets out there. It's reasonable to suppose that our conditions are not that uncommon, and there might be an order of magnitude more Earth-like planets.

There also would be millions of planets that are much harsher than Earth, yet perhaps some form of life could have evolved.

A counter argument might be that even our world was not always friendly to life; during Earth's first billion years it was quite a harsh place indeed. Subsequently there were several mass extinction events, the last one a mere 60 million years ago. During pre-Cambrian times, it's believed the planet was basically a giant snowball. Alien probes sent here during those periods might have concluded that there was no sustainable life.

I think it will be a good 200 years before we can get out to some of our neighboring stars and investigate up close. Even the closest stars would take multiple lifetimes to get to using any current or upcoming propulsion technologies. Ultimately it will be some kind of intelligent robotic explorer that we send out as a kind of trans-generational emissary, that may come back to entertain our distant descendants with tales of foreign worlds. Sad that trans-light propulsion is nothing but a pipe dream, for now anyway.

Oh, you forgot, He loves us SO MUCH that he will torture us forever for behaving as we were designed...When I make something that doesn't work right I take it apart and fix it, or scrap it and make something else...In no case do I put it on my barbeque grill forever.

Contrary to popular belief among religious fundamentalists, most atheists are not anti-Christmas. It has become more of a cultural holiday than a religious one anyway; If you asked 100 people at random what Christmas was about, how many do you think would say "the birth of Christ", and how many would say "presents", "family" or "Santa Claus"?

The people screaming bloody murder about nativity scenes and whatnot are a small but vocal minority. Usually those zealous types are former Christians themselves, the rest of us don't really care.

Which is of course, a pagan holiday, so distinctly not atheist.
How about a real atheist name?
Midwinterfest?

Well you could just continue the "Yule" tradition, as that's what's it still called up here in the cold north (i.e. the nordic countries); Jul. Pronounced pretty much like "Yule" [wikipedia.org].

So, even if your(?) ancestors had to resort to exporting Christianity all the way up here to solve the Viking problem, they couldn't dethrone the name for the seasonal festivities. It's time for us Viking ancestors to export it right back I say.:-)

Maybe, but it's pretty obvious that the GP to your post is anti-Christian.

Really? I got the impression that it was more anti-evangelical-megachurch. You know, the ones with the guy on TV wearing a $1000 suit, gold wristwatch, and so forth, begging for your money "GIVE! GIIIIIIVE UNTIL IT HUUURRRTS!" so that you can get your ticket into heaven, and he can make the next payment on his $million yacht where he has cuban rent-boys "lift his luggage".

It's perfectly possible for someone to not be anti-christian, and still think those hypocrites are worthy of scorn. I knew a minister in the United Church who would make jokes about those guys.

It's anecdotal, true, but I don't see an "atheists are sooo stupid, can't even see the hand of god in the universe" post on every other Slashdot article - but I *do* see "christians are sooo stupid with their imaginary invisible magic man" posts everywhere. I'm not sure how this makes atheists more generally tolerant than christians. In fact, multiple public posts on unrelated articles calling people stupid for the things they believe in is pretty much the opposite of tolerance...

Looking at polls of the population at large, atheists are among the least trusted groups of people. They are less trusted than Muslims, queers, and dope smokers, but more trusted than pedos, and presumably other 'harder' criminals.

Face it, religion is a business. Same as any others, the corner stones are money and power. Only difference to any other ordinary business is that the priorities are reversed.

Yeah, because Tim Tebow makes a fortune doing his charity and missionary work. That whole football thing is just a ruse. Of course, we all know that Tebow, or Colt McCoy or even Baylor's Robert Griffin III would never complete a pass if they didn't serve their time serving others. The receivers would simply refuse to catch the ball. For that matter all the people who sell all their belongings to go help the poor in destitute parts of the world are making a huge investment, trading their belongings for unlimited power and wealth.

I'm not saying that there are not those that use religion as a business, but they are the exception, not the rule. For every megachurch you see on TV, there are thousands of small town, churches full of people who are not there for money and power. Turn off the 700 Club and go see what real religion is all about. It's not on TV.

The Crusades, Inquisition, the Thirty Years' War, the Jihad, 9/11 are just a few examples of what God-fearing people can do. Religion is one of, if not the biggest causes of war and violence. People were fucking burned alive for thought-crime - belonging, or merely being accused, to another religion or to none.

How 'bout Einsteins "Magic Man in the Sky"? I recall his profession to the effect of "not believing that there 'couldn't' be a God".

The whole quote: I believe in Spinoza's God who reveals Himself in the orderly harmony of what exists, not in a God who concerns himself with fates and actions of human beings.

By Spinoza's God he basically means nature, not a religious god. It's hard to resist using Einstein as an authority, but religious people keep missing the boat there. Einstein did not believe in an omniscient god.

For instance, I know that time is relative. If Genisis' time-frame is relative to Gods perspective we can accept the possibility of 7 days to

Same applies to 7 seconds or 7 millennia. If you propose that the scale is meaningless, so is any argument referring to it,

yesterday I even saw something about rats having

empathy).

Yes, that was interesting. How come they can't go to heaven then? But people are more concerned about their dogs. If lawyers can go to heaven, why not dogs?:) Human traits like awareness and morality in animals is something most theists would consider the highest form of heresy.

Like Thomas Jefferson, my faith is know only to me

and my creator and it involves questioning everything, differentiating between thoughts,feelings,knowledge and belief.

Jefferson rejected the church. While he did sustain a belief in a higher entity, I tend to believe that were he alive today, with the body of science that we have discovered since his time, it's likely that he would reject this as well.

Maybe Einstein was on to something there.

I tend to side with his (Spinozan) humanist notion that the likelihood of the religious god is close to nil. It's unfortunate that people, even great people, associate the wonders of nature with a concept that is so easily misused. Which is why I avoid it.

The argument that it is impossible to disprove something does not support the argument, it is a statement of uncertainty. There are many things that are uncertain, almost everything in fact. This doesn't have us running around believing in the infinite number of extremely unlikely things. Nor should it. That there is a remote possibility of a god is meaningless in this context. See the teapot argument [wikipedia.org].

Even if the probability is infinitesimal, it only has to happen sometime, somewhere, and boom, here we are asking the questions. It's a lot more likely that "DNA just evolved" than "the magic man in the sky just appeared and was smart enough to create DNA".

Pardon in advance for any meanderings. Several interruptions while composing this.

And yet the Moon might well be the cause of several other factors.

The Moon is massive enough in comparison to the Earth that it is reasonable to consider the two to be a binary planet system in many ways. While the barycenter of the binary revolves around the Sun in a highly predictable ellipse, the Earth itself does not; it meanders inside and outside that elliptical orbit due to the Moon's influence. As a consequence, the location of the Earth's perihelion can shift more than one degree from one year to the next (varies from Jan 2 to Jan 4). The barycenter of the binary system is displaced from the center of the Earth toward the Moon by 75% of the Earth's radius (quick reference here [astronomycafe.net]), which from the point of view of a flat Earth theorist means that the barycenter is rushing along 1,000 miles beneath our feet at about twice the speed of sound.

And of course there are the tides.

Not just the ocean tides, but also the much greater tidal bulge of the atmosphere. And a definite tendency to a tidal bulge in the liquid core. IANAGeologist so I don't have a clue how the tidal forces and the weight of the mantle would interact... but then I think that most geologists have never considered this either since they are always looking down into the Earth and the Moon is for them a whoosh in the finest Slashdot meaning.

As far as evolution of life goes wrt planet Earth, the Moon is at the very least a major, significant stirring rod. It is really hard to say how major, since we are in the position of being stirred so everything else that is also being stirred with us looks very normal. It could be that both meteorology and geology need their Copernican revolution and won't really make sense until they meet their Galileos.

The better answer is to say that we don't know... because the likelihood of extraterrestrial intelligence that is typically used is only extrapolated mathematically from the information that we have. But because of the size of the data set that we have relative to the actual size of the cosmos, the probability for error in that regard is, by my understanding, roughly equivalent to anticipating the results of a random coin toss.

Simply put... we just don't know. And that's a *FAR* more truthful answer

While most planets are obviously not suitable for life, life itself has a strong tendency to overcome the challenges of its environment. Life endures climate fluctuations, extraterrestrial impacts, and even extreme radiation, all here on Earth. While many of these protective characteristics are conducive to the emergence of higher life, life itself has already shown its capacity to adapt and overcome.

Why do you think that life on other planets would have anything different from us resource and technology-wise? Unless you think the laws of physics and the Periodic Table of Elements are purely local to Earth? What we have now is whatever anyone else anywhere else would have. We won't have FTL spaceships, neither will they. Why is this so hard to understand? There's no Fermi's Paradox, there's only the Space Nutter Paradox: "Given what we know as FACTS, why would you think any other intelligent life would have more capacities than us?"

ah, it's the AC ignorant of science and engineering again. The only thing we've actually made leaps and bounds in is information processing, and that's MATH No, our fantastic IT is due to tremendous advances in materials science, you should learn how electronic devices such as undersea fiber optic systems and integrated circuits are made. We still burn fossil fuels in turbines in air or combustion chambers. That's it, that's all No, that is not all, where I live we get more than half our power from conversion of matter into energy. And a small company out in the western USA is making astounding advances in polywell fusion

It's not for visionless people like you to say what is and is not possible. That is for the engineer and scientist to say, people like me. You are consumer, "scrub load" as they say on submarines, users of our gifts.

Your mistake is in assuming that the starter gun fired at the same time for everyone. That isn't true, we're late to the game. Other planets finished forming and starting up their life engines more than a billion years before ours did. The question is, where are those folks? They should have had plenty of time to fill the galaxy by now.

This is a big unfounded assumption. And while jump-starting life and moving bacteria around may turn out to be easy, moving animals the size of humans to a star system even 20 ly away is already known to be very, very hard. (I mean, mammals could not reach New Zealand for millions of years, and that's another continent, not another star.) And while colonizing deep space is a priority, persisting without a big chunk of rock in the immediate neighborhood is probably a pipe dream. So we should probably think of it as a planet-sized organism (like Earth with its biosphere) casting a seed (a generation ship) to a different star system. One needs to find a planet that's already ripe; being optimistic, there is one within a few dozen ly. One needs to build a big ass ship in deep space, capable of withstanding a several (or many) thousand year journey with a self-sustaining biosphere inside, so probably something like an asteroid several hundred meters in diameter. Then one has to accelerate the sucker with something at least as good as fusion and slowly crawl towards the goal. Just the travel itself is easily 100000 years, and building an ark is a tremendous job as well. Once arrived, colonists cannot hope to propagate again for hundreds of thousands or may be millions of years, since they don't have a planet backing them, so there is more downtime.

Think about what I like calling a "hop time": the mean duration needed for a generation ship to colonize a planet, build a new generation ship, and travel to the next system. It's gotta be pretty big, may be a million years, may be 10. So if someone has a billion years on us, they may be on their 100-1000th hop. They are but a smidgen, may be as big as the width of the galactic disk. And if they are on the other side of the galaxy, we may not run into them for another few billion years.

Your mistake is in assuming that the starter gun fired at the same time for everyone. That isn't true, we're late to the game. Other planets finished forming and starting up their life engines more than a billion years before ours did. The question is, where are those folks? They should have had plenty of time to fill the galaxy by now.

Thing is that mankind only arrived on the planet *very* recently in evolutionary terms. In addition to this, we've made incredibly fast levels of progress in the past few thousand years, and the past hundred years has seen technological change orders of magnitude faster than *that*.

It's fair to assume that this process hasn't stopped yet- the logical conclusion some have drawn is the "singularity". Well, whether or not that happens, the bottom line is that we're in the middle of a change that's happening incredibly suddenly- the blink of an eye, the flash of a camera bulb- compared to the relative "hours" or "weeks" that life has existed on the planet overall.

Now, there *may* be a significant number of other worlds that are presently capable of supporting life out there, i.e. at the same time as ours. But even if there are (e.g.) hundreds of them, even if they *broadly* follow the same trajectory and timescale as earth (in terms of the evolution of life), even if their development was congruent to ours in the larger scale of things, the chance of even one other world's "camera flash" evolutionary moment occurring at exactly the same time as ours is incredibly small.

This matters because if they're even slightly behind, they're probably still at the monkey-level intelligence stage (if we're lucky), or the stage earth was at tens or hundreds of millions of years ago.

If they're even "slightly" ahead- e.g. a million years on the evolutionary scale of things is pretty "close" to us- then they're probably so far ahead of us that we won't even be able to begin to comprehend where they've gone, assuming their development (even if it eventually slowed down) went through the rapid phase that mankind is going through- and continued, even if only for a few thousand years!

This does assume that mankind's current rate of development can be continued at least for the immediate future. Still, I'm surprised that I haven't seen the above issue even considered elsewhere. Maybe I overlooked something obvious?

No, your theory has definitely been considered by many. Technological singularity changing the priorities of the civilization and/or rendering it invisible is definitely a possible explanation for the missing gating factor. That escape from the universe might be possible with a technology only slightly ahead of our own would explain everything (because this universe with its stupid second law of thermodynamics is a dead end that any reasonably advanced civilization would WANT to leave).

Heck, what's so unknown about it. There's a high probability that given enough technology, and one batshit insane looney, and it's the end of the line. We always seem to go under the theory that alien life wouldn't ever have any psychopaths, that it's somehow distinctly human to go nuts.

The actual science says there were stars with planets with elemental compositions like ours dating back about a billion years before our star. Everything after the third generation of supernovae had access to the right mix of elements, we just happen to be in the middle (as you'd expect, statistically) of the fourth generation. Now had we been near the beginning, one might more reasonably make the argument that we could be first. But this late in the game, that just doesn't seem likely.

No FTL? That's a proven fact - how? Those who assume that no possible sentient beings throughout the galaxy have ever built an FTL also ASSume that our knowledge of physics is flawless.

What we need is another bizarro, like Einstein, to stand the world on it's head. Someone who can look at all those computations, spot a couple of mistakes, draw a few conclusions, and come up with a hypothesis. What if, Einstein were only 85% correct?

I'm not about to go out on a limb, and say that FTL_is_possible, but neither will I go out on your limb, and say that FTL_is_not_possible.

I think - not a statement of fact, but an opinion - that FTL is probably possible. There are at least tens of thousands of questions to be answered before it becomes a reality, but I think it's possible. The energy required to power a ship large enough for a crew of ten, and say a hundred passengers would be more than astronomical - but possible.

And, do you know what? The jury is still out. You can't prove the impossibility, any more than I can prove the possibility. We'd get the same mileage arguing whether there is a god or not.

Life does not necessarily equal an advanced technological civilisation that we could detect or understand, not to mention that there's plenty of theories that may account for Fermi. The Doomsday argument [wikipedia.org] and the Singularity [wikipedia.org] are just 2 possibilities. There's plenty more, the problem is that until we actually find another civilisation, evidence of one, or conclusively prove they don't exist now or haven't existed... then we're still left with the paradox.

Consider that in less than 500 million years, the earth will be too hot to support life. So that means there is a race, the 5 billion year race from when our solar system began to that extinction time. Maybe most other planets with life lost that race, before anything could overcome the limits of their sun's cooking their home world.

Us being the first is extremely improbable, unless there are factors operating that we don't understand. That's really the core of the paradox, everything we understand about the rules so far suggests there should have been many thousands of technologically advanced civilizations by now, for none of them to have come to existence implies either an unbelievable extreme of luck on our part, or a filter factor operating that we don't understand.

I can already hear the "intelligent design" folks jumping on this topic as proof that we aren't here through random chance but were assembled by some creator. Just as an FYI, the "rare earth hypothesis" [wikipedia.org] has been circulating in the scientific community for many years.

Actually - if there is a God, he could have created life on an infinity of worlds, and separated all the worlds intentionally. The absence or the presence of life and/or intelligent life that is visible to us has absolutely nothing to do with the existence of God. Nothing.

I'd bash stamp collectors as well if they actively worked to block the teaching of science in schools, denied funding for legitimate scientific research, and pushed their viewpoint through taxpayer funded faith-based initiatives [theocracywatch.org].

Stamp collectors actually help subsidize the US mail since they boost profits with minimal cost to the post office. What's not to like about them?

"In a sufficiently large (possibly infinite) universe, it really just doesn't matter how uncommon any (non-zero) probability event appears - It will still happen all over the place, over and over and over and over again."

This is based on mathematical extrapolation, and while provably true for an average event. The proof cannot be verified all events without utilizing parallel universes.

But uniqueness would not in *ANY* way constitute any sort of proof of the existence of a god or verifying a creationists point of view, even though some might think that it would.

Suppose for a moment that it were actually possible to discover that we were isolated in the cosmos... that we were "it", and that intelligent life was otherwise non-existent anywhere else. While that might seem to mean something to people, in the grand scheme of things, it really doesn't mean anything at all... any more than the fact that a lot of people think that the northern lights are pretty means something particularly profound and meaningful about the meaning of life or whatnot. The cosmos can exist entirely without any purpose or meaning to it at all, and our human nature to ask "why" would only be destined to remain perpetually unanswered. This is equally true whether we are unique or not.

Water is extraordinary. It is one of the few substances that is less dense as a solid than as a liquid. This is a property with significance for aquatic life forms as aquatic life would have somewhat greater difficulty surviving in cold climates without that property.

And yet you do have to prepare yourself for the fact that it is a possibility. Though the article doesn't say unique, just very rare. Which may be a way of saying, that of the 708 exo-planets so far identified, not a single one may be habitable by life. I believe that's why the topic has come up again now, as a response to the articles claiming we might have found a planet capable of supporting life (like this one [slashdot.org]).

"You know, the most amazing thing happened to me tonight. I was coming here, on the way to the lecture, and I came in through the parking lot. And you won't believe what happened. I saw a car with the license plate ARW 357. Can you imagine? Of all the millions of license plates in the state, what was the chance that I would see that particular one tonight? Amazing!"

Just because our "route" resulted in our "life" situation, doesn't mean that other routes couldn't produce equally valid and viable "life" conditions. We're not that special.

What's exciting about the recent exoplanet work is that we're actually filling in the first few parameters of the Drake Equation. We're getting a grip on how common planets are, and now how common it is for them to be (a) not gas giants and (b) in the right zone around the star. I think those two alone (combined with "how many stars are like ours", which we have known a long time), knock off a good four orders of magnitude - from hundreds of billions of stars in this galaxy to tens of millions that are 1) not short-lived stars ; 2) have non-gas-giants that are 3) in the "habitable zone".

We already know enough from extremophiles on earth that anything with liquid water, practically, is "habitable zone".

What we can get from just closer examination of our own solar system whether life NOT "as we know it" happens - did it arise in liquid methane, or floating about in Jupiter's atmosphere and all that. And if it does, how complex does it get?

These "special conditions" may not be necessary for *life*, but they may be necessary for it to bother (sorry, "have reproductive advantage") going past single cells, which biologists still consider a pretty Great Leap Forward.

It may well be; until we're not extrapolating from one data point, speculation is just entertainment. If it turns out complex life happens only every trillion stars and there's only one other in the "local group", ten million light-years from here, well...rats. Just ourselves to talk to.

Console yourself with this: it means our celebrities are even MORE important than we ever imagined. "Miss Universe", for instance, really IS Miss Universe!!

If our solar system is so special that it is one in a million then there are about 200,000 systems that are as special as ours in the Milky Way. Multiply this by 100 billion to one trillion galaxies and we are really not that special.

Now I like boobs as much as the next guy. As a matter of fact what got my mind started down the track is staring at alien boobs on all of my favorite SciFi movies and I started thinking to myself "You know, those are kind of weird as far as life is concerned".

I'll use life on our own planet as an example. Only mammals have boobs.

Other animals do indeed feed on another, there's a lot of really unappealing vomit sharing in many types of life and poop sharing in the insect world that I think would probably be more common among the stars (Slurm for example) as it's even more common here. There are nutrient transfers that happen on our planet that are different than the insect ones I just mentioned might be out there as well as some we haven't thought of, but I keep thinking of boobs, cause I think of them all the time, and I just don't see them as something that are likely to exist on alien babes. I'm not discouraging my favorite Sci-Fi writers by any means, whatever happens keep the boobs on your alien babes, but when I think of the possibility of meeting real alien babes it saddens me when I realize evolution is unlikely to have included boobs into the equation.

It seems that life, intelligence, and civilization are the things that we find most interesting, in ascending order, when discussing exobiology. And, in ascending order, much, much more difficult to achieve. In other words, simple life is almost common, complex life is rare, intelligence even rarer, and civilization the rarest of all. Each step requires more time, stability, and opportunities for differentiation, than the last.
A lot of the uniqueness of the Earth, according to the article, has to do with its suitability for developing land-based life. I wonder if achieving a land-based civilization is rarer than a liquid-based one. If there are aliens sending probes over here to investigate us, maybe it's to study this weird, land-based civilization.
I admit that one advantage to land-based life development is that it's much easier to form divided ecosystems on land than it is in an ocean. This could create more opportunities for divergent evolution, speeding things up if you want to see a particular result, like intelligent life. However, it seems to me that there could be situations on other planets that can create a similar effect in a liquid environment. Perhaps not common, but possible. My point is, it might be chauvinistic to focus so much on conditions that allow the development of land-based life. The other, hidden chauvinism is towards carbon-based life, but it's hard to blame ourselves for that since it's so difficult to figure out how other kinds of life could work.

Aliens don't stop because they are busy searching for INTELLIGENT life.

Dear Aliens,Don't be racist, Thank you.The People of Earth.P.S. Do as we say, not as we do.

Why did the human cross the road?Because he's still stuck on his planet and can't fly.

A human walks into a bar with some Uropian gas termite his shoulder. The bartender before he throws them out asks, "Where did you get that disgusting thing?"The gas termite says "On planet Water, these dumb fucks are everywhere."

Do you remember in High School the retarded kids and their classrooms? Did you ever go in them? Did you know the retarded kids? Don't feel bad, nobody did. You knew where they were though so God forbid you stumble anywhere near there and be mistaken for a retard. If retards spoke, you just ignored them. Well I hate to tell everyone, but Earth is the Retard Class of the Galaxy. There are plenty of Aliens out there that know damn well where we are. But do you see them coming here? They don't want any of that "retard" rubbing off on them. Oh sure, we get sightings and such, but nothing official. Do you know why? These are the Aliens that are throwing spitballs at us and calling us RETARDS and running the hell off before they end up in detention or suspended.

"Why?" do you ask????

Well imagine our Alien benefactors who waited breathlessly and patiently for us to come out to space and prove we are intelligent. Who do we send? A dog! Imagine that? So they do a mind probe to find out WTF it wants and it wants a bone. They consider the situation and just leave and chock us all up for being retarded.Word gets around you know. Yeah...that new planet..? It's retarded!

So you ask me, is Earth special? I say yeah, it's special alright, it's Special Ed.

Agreed. Because life evolved a certain way here, and under certain conditions, doesn't mean that it can't evolve in a different way elsewhere, on possibly more (or less) challenging conditions. As long as you have variations and some selection mechanism, you'll get evolution (within reasonable bounds, of course).

I think it would be hard to find another identical Earth with a Moon of the same size as ours, but on the other hand - life can appear under for us strange circumstances. Just look at the fumaroles in the oceans - they have a life that's different from what we really recognize usually.

However even if many planets out there are either like Venus (hot and dense atmosphere) or Mars (thin dry atmosphere) you may be able to see planets that are similar to earth from many aspects, even if they may have a more int

For that matter, most of the things in their list are very odd things to choose for a "Rare Earth" argument. Gas giants in the outer solar system- there's no reason to assume that they're rare. Plate tectonics are believed to be a symptom of planet size (so larger-than-Earth rocky planets should have it), and several of Jupiter's moons show tectonic-style surface patterns. A magnetic core- ditto to planet size (where a solid core needs to be formed by pressure), with a possible proviso on planet age and planet chemical composition (influencing how long the core would take to cool). As there are only two Earth-sized planets in the Solar system, it's almost impossible to draw conclusions about frequency of occurrence.

The Moon is just about the only item in that list which I can agree with as being "rare", and as you say, its influence is debatable.

The Moon is just about the only item in that list which I can agree with as being "rare", and as you say, its influence is debatable.

For life to evolve, requires a changing environment. Without the moon's tidal effects, there would be a lot less dynamic events happening on the Earth. (I agree there still would be a magnetic field and plate tectonics; however, perhaps both of those were a result of the collision [wikipedia.org] of pre-Earth and Theia which created the moon.)

Additionally, one effect the moon had when it was closer (it's moving away at a rate of 1.5 inches per year, we know thanks to the reflectors placed there in the 60s which scienti

The whole point of the Fermi paradox is that if the earth isn't special, then where the hell is the evidence of alien life? All these posts explaining how we aren't special, and how "life will find a way", just lead right back to it. Why haven't we found so much as a single piece of evidence of any kind?

Probably because the lifespan of technological civilizations isn't that long. Human civilization is about 3000 years old, but only about two centuries of that is technological civilization with enough power to do much. We've had the ability to send radio signals into space for less than a century. We're already starting to run out of natural resources. There are arguments over how many decades are left for some resources, but nobody sees many centuries of resources left. Trying to mine low-density resources requires greater energy inputs for the results obtained, and eventually that stalls out.

If our understanding of physics is roughly correct, fast interstellar travel is hopeless. Slow interstellar travel might be possible, but it currently looks like the closest interesting place is about 500 light years away. Sending a generation ship to a system with no habitable planets is pointless. Sending one to an active civilization means it gets there after they've run down.

If you plug reasonable values for extrasolar planets into the Drake equation [pbs.org] and set the lifespan of a technological civilization to 500 years, you get 24 civilizations currently active in the Milky Way galaxy, which is about 100,000 years across.